Today, dependence upon drugs of addiction causes major health problems worldwide. For example, alcohol abuse and alcohol dependency can cause liver, pancreatic and kidney disease, heart disease, including dilated cardiomyopathy, polyneuropathy, internal bleeding, brain deterioration, alcohol poisoning, increased incidence of many types of cancer, insomnia, depression, anxiety, and even suicide. Heavy alcohol consumption by a pregnant mother can also lead to fetal alcohol syndrome, which is an incurable condition. Additionally, alcohol abuse and alcohol dependence are major contributing factors for head injuries, motor vehicle accidents, violence and assaults, and other neurological and other medical problems.
Addiction to nicotine is estimated by the National Institute on Drug Abuse to kill nearly 500,000 Americans every year. This total represents about 1 in 6 of all deaths in the U.S. caused by any means, and is more than the total of deaths caused by use of alcohol, cocaine, heroin, suicide, car accidents, fire and AIDS combined. Cigarette smoking is the most popular method of using nicotine, but there are also smokeless tobacco products such as snuff and chewing tobacco.
Nicotine addiction is linked to disease states such as leukemia, cataracts, and pneumonia; it is the cause of about one-third of all cancer deaths, the foremost of which is lung cancer. In addition to cancer, cigarette smoking also causes lung diseases, such as bronchitis and emphysema; it exacerbates asthma symptoms, and is the cause of chronic obstructive pulmonary diseases in general. It is also well known that cigarette smoking increases the risk of cardiovascular diseases, including stroke, heart attack, vascular disease, aneurysm, and the like.
Another major health problem is caused by cocaine abuse. Physical effects of cocaine use include constricted blood vessels, dilated pupils, and increased temperature, heart rate, and blood pressure. A user of cocaine can experience acute cardiovascular or cerebrovascular emergencies, such as a heart attack or stroke, potentially resulting in sudden death. Other complications associated with cocaine use include disturbances in heart rhythm, chest pain and respiratory failure, seizures, headaches, and gastrointestinal complications such as abdominal pain and nausea. Because cocaine has a tendency to decrease appetite, many chronic users can become malnourished. Repeated use of cocaine may lead to a state of increasing irritability, restlessness, and paranoia. This can result in a period of full-blown paranoid psychosis, in which the user loses touch with reality and experiences auditory hallucinations. Moreover, it is well known that the concurrent abuse of nicotine, cocaine and alcohol is common. It has been found that the combination of cocaine and alcohol exerts more cardiovascular toxicity in humans than either drug alone.
Historically, treating chemical dependence largely involved attempts to persuade patients to discontinue use the substance voluntarily (behavioral therapy). However, cocaine, morphine, amphetamines, nicotine, and alcohol, and other types of dopamine-producing agents are highly addictive substances, and dependence upon such drugs can be harder to break and is significantly more damaging than dependence on most other addictive substances. In particular, alcohol, cocaine, and heroin dependence are typically chronic relapsing disorders.
There has been some moderate success in providing effective treatments for tobacco addiction by the use of nicotine replacement therapy, such as nicotine gum or the nicotine transdermal patch. Additionally, antidepressants and antihypertensive drugs have been tried, with modest success. Attempts have also been made to treat tobacco addiction by persuading patients to discontinue the use of tobacco voluntarily (behavioral therapy), but this method has not proved to be very successful. Accordingly, it is clearly desirable to find a treatment for tobacco addiction that reduces or prevents the craving for nicotine that does not involve nicotine replacement therapy or the use of antidepressants and antihypertensive drugs.
Accordingly, there has been much interest in the scientific community in attempting to find substances that could be employed to ameliorate dependency on addictive agents. Compounds that have previously been employed for the treatment of alcohol abuse include disulfiram (Antabuse™), cyanamide, naltrexone; and acamprosate.

Naltrexone, a classical opiate antagonist, appears to act by reducing alcohol craving in abstinent patients. The drug, however, is hepatotoxic and causes side-effects that often require medical intervention. Acamprosate, another approved drug, is thought to act by modulating glutamatergic systems. It only has moderate efficacy and serious side effects that include diarrhea, allergic reactions, irregular heartbeats, and low or high blood pressure. Disulfiram, an aldehyde dehydrogenase inhibitor, acts by interfering with the metabolic pathway of alcohol. Normally, alcohol is metabolized to acetaldehyde, which in turn is eliminated by oxidation to acetic acid by the enzyme aldehyde dehydrogenase. Disulfiram inhibits aldehyde dehydrogenase and thereby prevents oxidation of alcohol-generated acetaldehyde to acetic acid. Alcohol consumption during disulfiram treatment, however, leads to the accumulation of acetaldehyde, inducing unpleasant side-effects. Because disulfiram does not reduce craving for alcohol, success with the drug depends on a high level of patient motivation since patients who wish to drink can simply stop taking the drug. Additionally, it has been recently proposed that disulfiram can be used for the treatment of cocaine dependency (for example, see Bonet et al., Journal of Substance Abuse Treatment, 26 (2004), 225-232).
Recently it has been shown that an isoflavone known as daidzein and structurally related derivatives thereof are effective in suppressing ethanol intake. Daidzein is the major active component obtained from extracts of Radix puerariae, a traditional Chinese medication that suppresses ethanol intake in Syrian golden hamsters. See Keung, W. M. and Vallee, B. L. (1993) Proc. Natl. Acad. Sci. USA 90, 10008-10012 and Keung, W. M., Klyosov, A. A., and Vallee, B. L. (1997) Proc. Natl. Acad. Sci. USA 94, 1675-1679, and U.S. Pat. Nos. 5,624,910 and 6,121,010. U.S. Pat. Nos. 5,624,910 and 6,121,010 disclosed ether isoflavone derivatives of daidzein, which were shown to be effective in treating ethanol dependency.
Mechanistically, daidzein and its derivatives were shown to be potent and selective inhibitors of human mitochondrial aldehyde dehydrogenase (ALDH-2), which is an enzyme involved in the major enzymatic pathway responsible for ethanol metabolism in humans. It appears preferable that daidzein analogues inhibit ALDH-2 selectively relative to the monoamine oxidase (MAO) pathway because daidzein analogues that inhibit both ALDH-2 and MAO exhibited less antidipsotropic activity. Alternatively, WO 2008/014497 disclosed novel isoflavone derivatives that are selective ALDH-2 inhibitors with little effect on the MAO pathway and, thus, are useful for the treatment of alcohol dependency.
In view of the above-indicated discoveries, a demand has emerged for additional classes of compounds that are safe and effective for the treatment of alcohol dependency, but that are structurally distinct from disulfiram, cyanamide, naltrexone; acamprosate, daidzein, and analogs thereof. Ideally, such additional classes of compounds will also be useful for the treatment of other addictive agents such as cocaine, heroin, and nicotine, and in particular, ameliorate the tendency of abusers to relapse.